1. FIELD OF THE INVENTION
The invention relates to a magnetic resonance apparatus, comprising a magnet system for generating a steady magnetic field, a coil system for generating gradient fields, and at least one RF coil which comprises a circuit with at least a self-inductance and a tuning capacitor, which circuit is tuned to a predetermined frequency and connected to first and second input terminals of an input amplifier of a receiving device for RF signals.
2. DESCRIPTION OF THE RELATED ART
An apparatus (MR apparatus) of this kind is known from, for example U.S. Pat. No. A-4,737,718 . Apparatus of this kind are customarily delivered together with a set of phantoms which can be used to check the imaging quality of the RF coils and the entire MR chain. The phantoms serve to simulate the presence of an object to be examined, for example a patient. They are used during installation of the apparatus, during fault-finding in the MR chain, during adjustment of the RF coils and the MR chain, and during image quality tests to be performed at regular intervals. A phantom usually consists of two segments, that is to say on the one hand a segment containing elements which can be imaged by the MR apparatus and which can serve to measure parameters which are decisive in respect of the image quality (for example, signal-to-noise ratio and uniformity), and on the other hand a segment which simulates the loading of the RF coil by the patient. This is because said parameters are co-determined by the coil quality Q arising from the RF coil itself and the coil load caused by the patient. Thus far, the load segment is customarily constructed as an annular vessel which is filled with an electrically conductive liquid (for example a saline solution) or as a closed circuit which can be inductively coupled to the RF coil and which may comprise, for example a coil, a resistor and a capacitor. Examples of such load phantoms are described in The British Journal of Radiology, 59, pp. 1031-1034. Generally speaking, a separate load phantom is required for each RF coil associated with the MR apparatus. The known phantoms of the described constructions are often comparatively voluminous, complex and difficult to handle. Moreover, they may be vulnerable and expensive.